In order for it to be possible to always operate an internal combustion engine in as optimum a manner as possible under different operating conditions, a very wide variety of methods are already known from the prior art. For instance, the variation of the valve opening duration is described in WO 2011/032632 A1. A camshaft comprises a hollow outer shaft and an inner shaft which is arranged such that it can be rotated concentrically within the outer shaft. A first part cam of a cam is mounted fixedly on the outer shaft so as to rotate with it, and a second part cam of the cam is connected fixedly to the inner shaft so as to rotate with it and is mounted rotatably on the outer shaft. The cam contour of the cam and therefore the valve opening time can be varied accordingly by way of rotation of the two-part cams with respect to one another, brought about by way of a rotation of the inner and outer shaft with respect to one another.
Each part cam requires a minimum axial installation space which is substantially as great as the installation space which a cam of a non-adjustable camshaft requires. Since, however, at least two part cams of this type are now to be provided per valve, the axial installation space which is required by the cams is increased overall.
The camshafts which are discussed here are to be distinguished fundamentally from camshafts of the type which comprise exclusively cams of the type, the contour of which is not variable. Although cams of this type can also be held variably on the camshaft, only the opening period can be shifted by way of this, but the duration thereof cannot be changed.